1. Field of the Invention
The present invention relates generally to an intake air flow rate control system for an internal combustion engine of an automotive vehicle. More specifically, the present invention relates to a control system for controlling an intake air flow rate in the engine idling condition, wherein the vehicle's transient operating characteristics can be improved in response to variation of required air flow rate corresponding to variation in throttle valve angle of the vehicle.
2. Description of the Prior Art
In recent years, pollution of the atmosphere by nitrogen oxides NO.sub.x, carbon monoxide CO, gaseous sulfurous acid and the like, as produced in the exhaust gas of automotive vehicles, has become a serious social problem. In addition to this, the price of fuel, i.e. gasoline or petrol, for automotive vehicles has become higher and higher, because of the limited resources thereof. For preventing atmospheric pollution caused by exhaust gases of automotive vehicles and for economic usage of fuel, it has become necessary for current automotive vehicles to control engine speed accurately even when the vehicle engine is idling.
In an air flow rate control system, when the vehicle starts driving after idling, required air flow rate through an idle port passage and a bypass passage for delivery to the intake manifold of the internal combustion engine is considerably increased. On the other hand, when the vehicle is rapidly decelerated and therefor the throttle valve is completely closed, required air flow rate is increased a considerable rate. For the conventional control system, it is impossible to follow such substantial changes in required air flow rate. Therefore, response to change of the required air flow rate is necessarily delayed. Indeed, in the conventional system, the air flow rate is varied gradually at a given rate to follow the change of required air flow rate. However, when the difference of the air flow rate between the present rate and the required rate is quite large, particularly when the required rate is too large relative to the present rate, it is impossible for the conventional system to follow the changed requirements rapidly. Therefore, conventional systems may possibly cause engine stalling under such circumstances.
On the other hand, in situations of response to increased air flow rate corresponding to rapid deceleration of the vehicle, and therefore in response to closure of the throttle valve, various systems have been developed to improve response characteristics corresponding to change of required air flow rate, such as a so-called dash-pot system. In the conventional system, the throttle valve is provided with a bypass passage with a valve means which is opened in response to excessive intake vacuum in the intake manifold. In this system, the vacuum in the intake manifold is measured sequentially and when the vacuum reaches a given value, a control command is applied to open the valve means to deliver the intake air through the bypass passage. However, in such a system, since the control for adjusting the air flow rate is made in response to exceeding of the air flow rate relative to that of required, delay of response is an inherent characteristic.
The present invention is intended to solve the above-mentioned difficulties or disadvantages in the prior art by providing an improved system for responding to varying of required air flow rate.